MACROBENTHIC BIODIVERSITY
Biodiversity as a modulator of ecosystem processes has been the basis of many ecosystem function studies (Loreau et al. 2001), but the focus has been exclusively on the use of species richness (Chapin et al. 1997, Bengtsson 1998). Due to their size, even within the same site, differences in environmental pressures may still be experienced due to different small-scale niches (McClurg 1996, Levin et al. 2010).
MEASUREMENT OF BIODIVERSITY
McClurg (1988) recognized an interesting relationship between the benthos distribution and the three sediment zones described by Flemming and Hay (1988) from the KZN Bight continental shelf. In particular, the taxonomic differences in the northern part of the Bight (stations F to I) would show greater diversity than the southern part (stations A to E).
AGULHAS CURRENT AND KZN BIGHT MACROBENTHIC DIVERSITY
ENVIRONMENTAL INFLUENCES ON MACROBENTHIC BIODIVERSITY ….8
We hypothesized that biodiversity patterns of macrobenthic communities in the KZN Bight mid-shelf were related to the key environmental parameters measured in the study. This might have been possible in the northern section of the KZN bay, as evidence of reef-building fauna (Cnidaria and Polychaetes: Serpulidae) was found.
KZN BIGHT WATERS AND THE AGULHAS CURRENT
The Agulhas Current has a seasonally dependent surface temperature and the KZN Bay water temperature reaches 25ºC in February and for the upper layers of the offshore region > 26ºC (Schumann 1988). According to Pearce (1978), the annual temperature range of the coastal waters is 4.8ºC, with an average seasonal variation of 5ºC.
SEDIMENT HABITAT OF THE KZN BIGHT
And it is here, east of Durban, that the sediment changes from the normal trend of onshore and outer shelf terrigenous gravels to one that has a terrigenous belt extending across the shelf to the shelf break (Heydorn 1976, Bosman et al. 2007). At the center of this deposit is a meandering section of mudstone that also extends along the shelf from Tugela Gorge to Tugela Canyon (Heydorn 1976).
COLLECTION, PREPERATION AND ENUMERATION
Each grab sample had to have a minimum sediment depth of 5 cm to be an adequate representation of the station. The rest of the bucket volume was filled, with seawater, stirred for one minute and the suspended fauna was poured through a 1000µm sieve.
STATISTICAL ANALYSIS
The North KZN Boog midshelf (from station F to I), although predicted to be low diversity as suggested by commonly used alpha diversity indices and abundance (m-2), was in fact not, due to of possible greater turnover (taxonomic diversity) in this section of the Bight compared to the section south of station E. Different environmental variables were important in explaining the abundance and diversity between the Southern and Northern parts of the KZN Bight.
RESULTS
Thus, at all scales measured, beta diversity reflected the same pattern along the midshelf of the KZN bend. Arthropoda had the most even and less drastic change in turnover rate in the middle of the KZN bend.
DISCUSSION
Of the four phyla, Cnidaria had the sharpest increase in turnover across the KZN bay from the South DF to the North RBF. This was consistent with some of the highest benthos soft sediment species richness found (Gray 1997a). The pattern of beta diversity found could have been a reflection of the different relative contributions of local and regional species contributions.
A similar study by Williams et al. 2010) on the southeastern continental margin of Australia, found that 57% of the macrobenthic fauna found were possible new species.
INTRODUCTION
Arabian Sea a unique range of environments influences the diversity of that macrobenthic community (Jayaraj et al. 2007). Continental margins receive significant inputs from rivers such as floodwater, macrophytic debris, suspended organic matter and all kinds of debris (Levin et al. 2010). The impact of organic matter on macrobenthic community structure has been found to be more complex because the interactions between micro-, meio- and macrobenthic fauna are more complex (Quintana et al. 2010).
Different groups of marine organisms are therefore affected differently by different environmental processes (Snelgrove 1999, Jayaraj et al. 2007).
METHODS AND MATERIALS
Hierarchical group mean analysis based on Euclidean distance was applied to station environmental variables. Multivariate correlation and similarity analyzes were used to determine whether environmental variables were associated with macrobenthic community attributes. Spearman's rank correlation analysis was used to test for associations between biological characteristics (community abundance and diversity of the whole community and separate trunk groups) and environmental variables, and between the environmental variables themselves.
CONPLOT analysis found in the statistical software program Primer version 6 (Clarke and Warwick 2001) was used to visually assess differences between environmental characteristics of stations and to determine which environmental variables of biological communities were associated with designated stations.
RESULTS
Thus, there was a complex relationship between environmental variables operating at a certain scale of study and location within the Bay, which determined biological characteristics of the macrobenthic communities. Within the South Bight stations, abundance (m-2) was significantly explained (Rho 0.54, P < 0.05) by depth, temperature, % coarse sand, % medium sand and % very fine sand, while none of the diversity within this region could explained by environmental variables. Variation in diversity explained was lowest for Annelida (R2: 0.27, P < 0.05) within the North Bay and none of the other phylum group diversity could be explained by measured environmental variables from this region (Table. 4.7).
Macrobenthic communities in stations A, B, F and I were associated with high proportions of very fine sand and fine sand, with station F having the lowest amount of fine sand of the three stations.
DISCUSSION
Macrobenthic species distributions were found to be significantly correlated with the spatial distribution of sediment characteristics (Otani et al. 2008). The depth of the water column usually has a large influence on the sedimentation and dynamics of the dominant water in the region (Zalmon et al. 2013). Local and regional processes are involved in maintaining the coexistence of species in a community (Witman et al. 2004).
The way in which temperature, salinity, organic matter and sediments determine diversity depends on the aspect of the community being measured (Jayaraj et al. 2007).
CONCLUSION
Stations in the southern mid-shelf region of the KZN Bight had significantly (see Table 5.6) higher taxonomic distinction than stations located in the northern section of the Bight. However, most stations remained within the range of mean taxonomic distinction and variation in taxonomic distinction found of all Bight communities. Taxonomic distinction as a measure of diversity applied at a large scale: the benthos of the Norwegian continental shelf.
METHODS AND MATERIALS
Taxonomic diversity indices were tested for normality using the Shapiro-Wilk test of normality and the relationships between mean taxonomic distinction, variation in taxonomic distinction and species richness were determined using a Spearman rank correlation (ρ). Mean taxonomic distinction and variation in taxonomic distinction are independent of each other and each can provide important different information regarding community diversity and the factors that influence it (Arvanitidis et al. 2002). To determine whether communities along the Bight differed significantly from the expected taxonomic distinctness found in the KZN Bight mid-shelf, funnel and ellipse plots (mean taxonomic distinctness and variation in taxonomic distinctness pairs) were produced based on summed macrobenthic abundances (m -2 per). station, with 1000 maximum numbers of randomly chosen Species/phyla (sublists) for each M value (number of phyla) drawn from the master list of 1177 species when calculating statistics.
It indicated the expected mean taxonomic distinctness and variation in taxonomic distinctness at 95% confidence intervals by superimposing the observed values relative to confidence intervals and expected values.
RESULTS
Again, stations I, A and C were significantly different from the expected range of variation in taxonomic distinction found in the middle of the KZN Bight. The variation in taxonomic distinction (Ʌ+) was significantly greater within the South Bend section (see table). Variation in taxonomic distinction in the South Bend was approximately similar in trend to species richness up to station D.
Rank mean taxonomic distinction and variation in taxonomic distinction show approximately linear and constant relationships with rank percent finesand content.
DISCUSSION
In general, habitat types appeared to be the major role player in the establishment of taxonomic distinctness and trophic group diversity (Ellingsen et al. 2005). This may be due to the possible difference in community assembly types associated with the different environments in this section (Ellingsen et al. 2005). Off the southern Bay of Biscay, NE Atlantic, Spain, sediment characteristics were very important to play a role in the diversity of the macrobenthic communities (Louzao et al. 2010).
The processes involved in the creation of heterogeneity for each phylum must therefore be taken into account in conservation planning (Bevilacqua et al. 2012).
CONCLUSION
Macrobenthic taxonomic diversity and Whittaker's beta diversity were explained by different measured environmental variables compared to those that explained alpha diversity. Differences in the taxonomic diversity of macrobenthic communities in the southern and northern bay sections were not explained by the same measured environmental variables. No environmental variable could explain variation in taxonomic diversity in the South Bight section, and percent fine sand was the only variable that explained taxonomic diversity; this included the depth that explained the beta diversity in the North Bight section.
2012) using a modeling approach found that increased physical forcing increased the release of nutrients and organic matter, which stimulated the bacterio-plankton and phytoplankton parts of the sediment and water column interactions, and possibly such mechanisms could reduce the availability of nutrients support high taxonomic diversity in the North Bight.
THE WAY FORWARD
A review of the offshore crustacean trawl fishery on the east coast of South Africa. Measuring marine species diversity, with application to the benthic fauna on the Norwegian continental shelf. Ecosystem dynamics in the Pacific-influenced northern Bering and Chukchi Seas of the American Arctic.
Seasonal changes in digestive enzyme levels of the amphipod Corophium volutator (Pallas) in relation to diet.
